1. Field of the Invention
This invention relates to a method for the preparation of one-package, room-temperature-vulcanizable, (RTV) silicone elastomer compositions. More particularly, this invention relates to a method for the preparation of a one-package RTV silicone elastomer composition that prior to its cure is highly workable and that during its cure will not crack or fissure even when deformed by an outside force.
2. Description of the Prior Art
One-package RTV silicone elastomer compositions are in wide use as sealants, coatings, and adhesives for application to substrates, machinery, and devices in a number of sectors, such as the construction and civil engineering sectors, general manufacturing, and electrical and electronic sectors. The use of these one-package RTV silicone elastomer compositions involves their storage in a sealed container, such as a tube or cartridge; then, at the actual point of application, extrusion of the silicone elastomer composition as a paste; and thereafter finishing the surface to smoothness using, for example, a spatula. Thus, the surface of the composition must not cure for the particular period of time elapsing from extrusion into the atmosphere until finishing. Moreover, even when the surface has begun to cure, additional time is required for the curing region to develop adequate mechanical strength, and deformation of the composition by outside forces is problematic during the time interval extending from cure initiation at the surface until the development of mechanical strength. In specific terms, when subjected to a stretching or elongational deformation, the curing region will rupture due to its inadequate mechanical strength. This occurrence of rupture in one location can lead to fracture of the entire body after its cure due to stress concentration at the aforesaid rupture site.
The occurrence of rupture during the course of curing can be prevented by increasing the cure rate of subject silicone elastomer compositions, but simply increasing the cure rate functions to shorten the working time available for spatula finishing. The use of this approach is also associated with a ready tendency for the silicone elastomer composition to yellow during storage. Therefore, it is desirable to develop a one-package RTV silicone elastomer composition that exhibits an acceptable working time and still rapidly develops mechanical strength once curing has started.
Within the realm of one-package RTV silicone elastomer compositions, numerous compositions have already been proposed that use oxime group-containing organosilane as crosslinker, such as Toshiba Silicone KK in Japanese Patent Application Laid Open (Kokai or Unexamined) Number Hei 2-41361, published Feb. 9, 1990; Shinetsu Chemical Ind. Co in Japanese Patent Application Laid Open Number Hei 4-353565, published Dec. 8, 1992; Arai et al in U.S. Pat. No. 5,266,631, issued Nov. 30, 1993 (based on Japanese Patent Application Laid Open Numbers Hei 4-366171 (1992) and Hei 5-105813 (1993); and Japanese Patent Publication Number Hei 4-53902 [53,902/1992]. These compositions evidence low invasiveness into the adherend and excellent storage properties. This prior work provides numerous examples that use vinyltrioximesilane or methyltrioximesilane as the oxime group-containing organosilane and also gives examples in which these two crosslinkers are used in combination. However, this prior work cannot solve the problems described above.